Fats and fatty oils, commonly called triglycerides, are constituted of triesters of glycerol, and include minor amounts of fatty acids. At ambient temperatures, about 20 degrees Celsius to about 25 degrees Celsius, fats are solids, whereas fatty oils are liquids.
Triglycerides are widely distributed in nature. Some triglycerides are edible while others are not. Many are derived directly from vegetable, animal, and marine sources. Others are obtained, as by-products, in the production of fiber from vegetable matter, and in the production of protein from vegetable, animal or marine matter.
Edible vegetable oils include canola, coconut, corn germ, cottonseed, olive, palm, peanut, rapeseed, safflower, sesame seed, soybean, and sunflower oils. Examples of nonedible vegetable oils are jojoba oil, linseed oil and castor oil.
Illustrative sources of edible animal-derived oil include lard and tallow. Examples of nonedible animal-derived oil are low grade tallow and neat's-foot oils.
Some of these oils may have a color that is objectionable to a consumer. Thus, the oil needs to be bleached to improve its color quality. To this end, a great many oils are commonly treated with bleaching clays to reduce oil color values by adsorptive purification. Bleaching clays generally improve oil color quality by selectively adsorbing color impurities that are present. Color impurities typically present in oils include, for example, carotenoids, xanthophylls, xanthophyll esters, chlorophyll, tocopherols, as well as oxidized fatty acids and fatty acid polymers.
It is also desirable to remove color impurities from a nonedible oil to obtain an acceptable color.
Natural clays, e.g., Fuller's earth and the bentonites, have commonly been used as bleaching clays to remove both the naturally-occurring and the otherwise-present, e.g., the thermally-induced, color impurities from edible and nonedible oils. It has been suggested that clays containing a zeolite can be used for such a purpose as well.
Acid-activated clays have also been used for this purpose. Such clays generally remove a relatively wider spectrum of color impurities. However, there has been no way of predicting which clays have properties that make them preferable for acid activation methods.
A conventional process for producing acid-activated bleaching clays utilizes calcium bentonite clays and sulfuric acid. The calcium bentonites used in the acid activation process typically are neutral to mildly basic. The acidic salts formed during activation and residual acid can be washed off and separated by filtration from the product clay, if desired. However, it is not necessary to do so.
Other suitable naturally-occurring clays are the palygorskite clays. Mineralogically, the palygorskite (attapulgite) clays are distinguishable from the bentonites (smectites, including montmorillonites).
What is needed is a way to identify clay minerals that are readily susceptible to treatment with acid to produce a useful bleaching clay product suitable for adsorptive purification of an oil. Furthermore, what is needed is a method of manufacturing a bleaching clay product that has enhanced surface acidity and that provides product efficacy for purification, e.g., bleaching, of an oil.